Material classifier



n- 1948- G. B. EBERsoLE ET AL 2,434,037

MATERIAL CLASSIFIER Filed April 2, 1943 5 Sheets-Sheet 1 A ITORNE Y1943- I r G; B. EBERSOLE arm. Q037 MATERIAL CLASSIFIER Filed April 2,1943 5 Sheets-Sheet 2 INVENTORS George B. Ebersole f BY Lester L. LeachATTORNEY Jan. 6,1948. e. B. EBERSOLEIEI'AL. 2,434,037

v MATERIAL CLASSIFIER Filed April 2, 1943 3 Sheets-Sheet 3 Fig. 3

37 2 5/ I 3 pr" INVENTORS Geo rge 'B. fbersole 1 BY LesterLLezc/z ATTORNE Y Patented Jan. 6, 1948 7 2,434,037, MATERIAL CLASSIFIER GeorgeB. Ebersole, Akron, and Lester Barberton, Ohio, asslgnors to The Babcock8rv I Wilcox Company,

tion of New Jersey Rockleigh, N. J., a corpora- Application April 2,1943, Serial No. 481,518

4 Claims. (01. 209-139) I The present invention relates in general tothe construction and operation of stationary classifiers adapted toselectively separate solid particles in suspension ina gasstream, andmore particularly to classifiers of thistype adapted for use in theoutlet end of pulverizers in which the pulverized material is carriedout of the puverizing or grinding zone in suspension in a gaseouscarrier medium. The classifier of our invention is particularly designedand especially useful in pulv'erizers f the general type shown in U. S.Patent No. 2,275,595, in which the material treated is coal, phosphaterock,.and the like. In such pulverizers, the pulverizing elements arerelatively movable upper and lower grinding rings between which acircular row of grinding balls is horizontally arranged, and thepulverized material is removed from the grinding zone by an annularstream of carrier air passing upwardly through a restricted annularthroat and picking up pulverized material discharged from the outercircumferential edge of the lower grinding ring.

The. general object of our invention is the provision of a materialclassifier which is capable of effectively classifying suspendedmaterial at high capacity rates with a relatively low pressure dropthrough the classifier. A further and more specific object is theprovision of an air-swept pulverizer having a classifier of the typedescribed which is capable ofsubstantially increasing the circulatingload of the pulverizer while substantially reducing the air pressuredropthrough the grinding zone.

The various features of noveltyi which characterize our invention'arepointed out with-particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operatingadvantages andspecific objects attained by its use,reference should be hadv to the accompanying drawings and descriptivematter in which we have illustrated and described preferred embodimentsof our invention. I

0f the drawings:

Fig. 1 is a sectional elevation of a pulverizer incorporating astationary classifier constructed and arranged in accordance with ourinvention;

Fig. 2 is an enlarged horizontal section, partly broken away, taken onthe line 22 of Fig. 1; and

Fig. 3 is a sectional elevation of a portion of a pulverizer with amodified form of classifier, parts of the pulverizer being omitted forpurposes of clarity.

The classifier of our invention is illustrated in Figs. 1 and 2 asincorporated in the top :or outiii . 2 let section of an air-sweptpulverizer, the grinding parts of which are enclosed in a cylindricalcasing Ill. The pulverizer has a vertical drive shaft ll carrying agenerally conical drive yoke 12 on its upper end. A lower grinding ringI4 is mounted on flattened lower portions of the yoke and its surfaceshaped to form a track for a circular row of grinding balls I5. Thehalls l5 support a nonrotary upper grinding ring l6. An annular spiderI! mounted on the upper ring is provided with lugs l8 arranged invertical guides IS! on the inner wall of the 'casing III for preventingrotation, but permitting vertical movement, of the spider and upperring. A resilient grinding pressure is exerted downwardly-0n thegrinding parts by a number of coil springs 20 engaging the spider.

The material to be pulverized is supplied through a feed spout 2| to theinner side of the spider and upper grinding ring and falls on theinclined upper surface of the drive yoke 12, being distributedthroughout the grinding area by the rotation of the drive yoke andassociated parts. The material flows outwardly over the upper surface ofthe yoke and lower grinding ring, is pulverized between, the relativelymoving balls and grinding rings and discharges over the outer edge ofthe lower grinding ring at an oblique angle to the periphery thereofdepending upon the ring speed. I

- The pulverizer disclosed is of the airswept type having an annularstream of primary or carrier air passing upwardly at the discharge sideof the pulverizer grinding'zone and through astationary classifierhereinafter described to a central outlet 22 for the material laden airstream. A cylindrical turret 23 forms an upward continuation of theoutlet opening 22 and has one or more valve controlled discharge pipes24 symmetrically connected into the turret top plate, The carrier air isnormally preheated and supplied under pressure by a suitable forceddraft fan (not shown) to an involute wind box 25 surrounding the casing[0 opposite the grinding zone. The carrier air flows into the pulverizerthrough casing passages 26 at the outer side of the drive yoke and thenupwardly through an annular throat passage 21 formed between the outerside of the lower grinding ring and an annular throat plate 28 mountedonthe inner side of the casing. Relatively unpulverizable material, suchas pyrites, leaving the grinding zone drops through the throat and iscollected in a compartment 29 in the base section of the-pulverizer.

The material leaving the pulverizing zone includes a large percentage ofoversize or coarse bolts 33 extending are used in the embodimentparticles which must be returned to the pulverizing zone ior regrinding,ii the material distribution to the discharge pipes is to be of thedesired fineness and uniformity. Various types of classifiers of variousdegrees of effectiveness have been installed between the pulverizergrinding zone and discharge pipes for the purpose of selectivelyclassifying the suspended material and returning oversize particles tothe grinding zone. A relatively high percentage of returned material orcirculating load is desirable for optimum operation of pulverizers ofthis type. The return of rejected oversize particles to the grindingzone is hindered by the varying air pressure conditions in differentparts of the pulverizer, and particularly by the pressure drop throughthe classifier, necessitating the passage of rejected material from alow pressure zone to a higher pressure zone. A further normalobstruction to the return of rejects is the travel of the rejectedparticles across the path of now of the material laden air streamapproaching the classifier, which tends to cause previously rejectedparticles to be swept up and again passed through the classifier withoutintervening regrinding. I

The improved classifier of our invention is of the stationarytype andcomprises apair of frusto-conical members or truncated cones 3d and 3|arranged coaxially oi the pulverizer outlet 23. The outer cone 33 has atop flange 32 held in contact with the pulverizer casing top plate byeye through the top plate. The flange extends inwardly from the outercone to the perimeter of the outlet 22. The inner cone 3| is spaced fromthe outer cone a distance equal to the width of the flange 32, with itsupper end spaced therefrom to provide an annular opening 34 into thedownwardly flaring annular space 35 between the cones.

The lower part of-the space within the inner cone 3! is occupied by acentral hub or cover member 31 and a series of symmetrically arrangedoverlapping inclined segmental blades 38 extending radially from the hub31 to th inner side of the lower end of the inner cone 3|. Each of theblades 38 is inclined in a clockwise direction. Twelve'blades are shownand each blade when developed has a true angle of- 40, so that aconsiderable overlap of adjacent blades is provided. V

The annular opening 34 at the upper .end of the intercone space 35 isoccupied by a circular series of short inclined deflector plates 40symmetrically spaced circumferentially. Sixteen of such platesillustrated, each being inclined 45 in both plan and elevation, withthe'outer edge advanced in a clockwise direction. a The space 35 betweenthe cone members is di-c vided into three double chutes by inclinedplates 42, the lower end of each chute opening into a depending trap 43having a hinged flap valve or gate 44 at its lower end. The traps 43 areinclined inwardly sufficiently to bring their lower ends above the innerside of the ball row. A portion of the outer cone 30 is cut away toavoid obstructing the feed spout 2 l.

The effective flow area of the annular opening the lower end of theturret and adapted to be moved downwardly, as indicated in broken lines,to close ofi all or a part of the'opening 34. Externally adjustablesupport rods 41 are provided for this purpose.

When a pulverizer of the character described is used in a direct firedpulverized coal system, the

. amount of carrier air supplied is substantially dition of the largersize particles.

34 is made variable by a sleeve 46 positioned in rectly proportional tothe amount of coal to be pulverized. The air velocity in the throat willvary with changes in load, but at all times will be suflicient to liftthe pulverized material out of the pulverizing zone. Normally a mass ofpulverized material will be maintained in a. floating condition abovethe throat and from which the rising air stream continuously picks uppulverized material. The clockwise rotation of the pulverizer yoke andlower grinding ring tends to promote a swirl oi! the material laden airin that direction, so that the stream passing upwardly along the outerside of the upper grinding ring and spider will have a general clockwisemovement. In order to reach the pulverizer outlet 22, the material ladenair stream must pass through the passagesformed between the, stationaryblades 38 and due to the shape and inclined arrangement of these bladesreceives -a substantial additional swirling effect in a clockwisedirection which causes the larger size particles to be thrown outwardlytov outwardly into the op and in effect are skimmed ed the moving streamby the plates and enter the space 35, thereby increasing the averagefineness of the remaining particles in suspension. The amount ofmaterial so eliminated is proportional to the effective port area of theopening 34, so that the sleeve 33 can be adjusted to control that areaand thereby the effective time in which the oversize particles canseparate from the stream. The fineness of the suspended material passingto the turret and discharge pipes is thus.

variable.

The annular opening 34 also acts as an outlet for oversize materialseparating out of the stream when in the turret. Due to the substantialheight and cylindrical shape of tend to form in the upper part thereof,which together with the retarding action of the turret walls, have beenfound to effect further separa- 'These oversize particles dribble downthe sides of the turret wall and control sleeve and pass out through theannular opening 34.

The oversize or rejected material entering the intercone space 35 fallsdown the chutes therein to the traps 43, from which it dischargesthrough the flap valves whenever the head of material is suflicient toovercome the existing pressure differential between the pulverizing zoneand the interior of the classifier. The rejected material drops into thespace at the inner side of the ball row and again passes through thepulverizing zone.

The described construction and arrangement of the classifier has beenfound to result in the maintenance of a desirably high circulating loadin the pulverizer, while reducing the amount of material in flotationabove the throat substantially to the minimum necessary to operate theusual differential pressure control of the associated feeden. .Theselective separation obtained with the described classifier is highlyeffective in eliminating oversize material with little, it, any, addedfan power consumption.

In the modification illustrated in Fig. 3, the

the turret, eddy currents assaosr 5. increased and the level of thereject opening raised to more efiectively utilize the swirl effectcreated by the stationary blades 38. The general arrangement is similarto that in Figs. 1 and 2, with the body of the classifier formed byspaced inner and outer truncated cones 50 and 5| respectively enclosingan annular space 52 divided into chutes by inclined plates 53 leadingintofiap valve controlled bottom traps 54, The turret 60 is flaredupwardly and the inner cone member 50 provided with an upwardly flaringextension 5| to provide a continuation of the space 52. The upper end ofthe turret has a top plate 82 in which discharge pipes 53 aresymmetrically arranged. The inner cone extension 8i stops short of thetop plate 52 to provide an annular exit opening 65 for the rejectedmaterial into the annular space 52. An inverted irustoconical baflie 56is positioned at the inner side or the exit opening 65 to facilitate theseparation of material flowing along the surface of the extension member5l, while requiring an abrupt change in direction of material in theperipheral portion of the stream to reach the discharge pipes 53. Thebaiile 86 is supported from the top plate by rods 68 which areexternally adjustable to vary the position or the heme and thereby theeflective entrance area of the exit opening 85. The higher the positionor the cone, the greater will be the fineness of the material reachingthe discharge pipes.

While in accordance with the provisions of the statutes we haveillustrated and described herein the best forms 01. the invention nowknown to us, those skilled in the art will understand that changes maybe made in theform of the apparatus disclosed without departing from thespirit of the inventioncovered by our claims, and that certain featuresof our invention may sometimes be used to advantage without acorresponding use of other features. In the 'claims, theword air" isintended to generically cover any gaseous carrier medium suitable forremoving pulverized material in the manner described.

We claim:

1. A material classifier comprising a pair 01' vertically. extendinginner and outer upright frusto-conical casing members arranged'to forman annular space therebetween and inlet and outlet openings forair-borne material at the lower and upper ends respectively of saidinnercasing member, the upper part of said inner casing member being formedto provide a separate substantially annular entrance for oversizematerial into said annular space. stationary baille means in said inletopening constructed and arranged to swirl the entering air-bornematerial upwardly through said inner casing member, averticallyadjustable baiiie for varying the efiective height of said annularentrance, means subdividing at least the lower portion of said annularspace into chutes, and a valve controlled trap at the lower end of eachchute.

2. A material classifier comprising a pair of vertically extending innerand outer upri ht frusto-conical casing, members arranged to form anannular space therebetween and inlet and outlet openings for air-bornematerial at the lower and upper ends respectively of said inner casingmember. the upper part of said inner casin member being formed toprovide a, separate substantially annular entrance for oversize materialinto said annular space, means in said inlet opentrance, meanssubdividing at least the lower portion of said annular space intochutes, and a valve controlled trap at the lower end of each chute.

3. A material classifier comprising a pair of vertically extending innerand outer upright frusto-conical casing members arranged to form anannular space therebetween and inlet and outlet openings for air-bornematerial at the lower and upper ends respectively of said inner casingmember, the upper part of said inner casing member being formed toprovide a separate substantially annular entrance for oversize mate-'rial into said annular space, stationary baiiie means in said inletopening constructed and arranged to swirl the entering air-bornematerial upwardly through said inner casin member, deflector plates insaid annular entrance for de-' fleeting material into said annularspace, a vertically adjustable battle for varying the eflective area ofsaid annular entrance, means subdividing at least the lower portion orsaid annular space into chutes, and a flap valve controlled trap at thelower end of each chute.

4. In combination, a casing having an outlet in its upper end formaterial-laden air, and a stationary classifier positioned in saidcasing below and symmetrically arranged relative to said outlet, saidclassifier comprising spaced inner and outer upright irusto-conicalmembers relatively arranged to form an annular space therebetween havingan annular opening thereto above said inner frusto-conical member,stationary baifle means within said innerfrusto-conical memberconstructed and arranged for eflecting a swirl of enteringmaterial-laden air, deflector plates positioned in said annular openingand arranged to deflect material into said annular space, platessubdividing said annular space into chutes, a flap valve controlled trapat the bottom of each chute, and an adjustable sleeve bafilc arranged tovary the efi'ective area of said annular opening. GEORGE B. EBERSOLE.

LESTER. L. LEACH.

REFERENCES CITED in the UNITED STATES PATENTS Number Name. Date 857,988Fuller June 25, 1907 1,965,186 Hardgrove July 8, 1934 1,724,041 PlaistedAug. 13, 1929 452,580 Morse May 19, 1891 465,548 Shelley Dec. 22, 18911,214,249 Williams Jan. 30, 1917 2,079,155. Crites May 4, 1937 429,347-Haslrell June 3, 1890 750,088 Child Jan. 19, 1904 1,367,637 SturtevantFeb. 8, 1921 2,211,274 Kuck -1 Aug. 18, 1940 2,275,595 Schwartz Mar. 10,1942 2,087,645 Hermann July 20, 1937 FOREIGN PATENTS Number Country Date813,690 ca June 20, 1929

